1. Field of the Invention
The present invention relates to a scan-exposure device for scan-exposure of photosensitive materials such as printing plates with light beams emitted from light sources moving along a main-scanning direction or a sub-scanning direction.
2. Description of the Related Art
In some image exposing apparatuses, which expose photosensitive materials such as photosensitive planographic printing plates used for printing (hereinafter referred to as xe2x80x9cprinting platesxe2x80x9d), or the like, semiconductor lasers or LEDs are used as light sources, and printing plates are subjected to scan-exposure with light beams emitted from the light sources. Further, in some image exposing apparatuses, a printing plate is wound around a peripheral surface of a rotating drum, and then a main-scanning of the printing plate is carried out by rotating the rotating drum in a predetermined direction, and a sub-scanning is carried out by moving light sources, disposed to face the peripheral surface of the rotating drum, in an axial direction of the rotating drum.
In some scan-exposure devices provided in such image exposing apparatuses, a plurality of light sources are assembled with a predetermined spacing on an exposing stage which is disposed so as to face a peripheral surface of a rotating drum with a longitudinal direction thereof being parallel to a sub-scanning direction which is an axial direction of the rotating drum. In these devices, a sub-scanning with a plurality of light beams at a time is carried out by moving the exposing stage in the sub-scanning direction. That is, some scan-exposure devices are provided with an exposing head having a plurality of light sources arrayed in a line on an exposing stage.
By the way, when a printing plate is subjected to a scan-exposure by using a plurality of light sources arrayed in a line, focus adjustment of light beams irradiated from the respective light sources is also required. Therefore, in this exposing head, when light sources are attached at an exposing stage, they are adjusted so that spots of light beams emitted from the respective light sources are aligned in a line, the light beams emitted from the respective light sources being focused.
Further, the light sources are assembled to the exposing stage so that distances between the light sources and the rotating drum are the same at opposite end portions of the exposing stage. Thus, in the scan-exposure device having the light sources arrayed in a line, a light beam emitted from any one of the plurality of light sources is focused on a printing plate wound around the rotating drum.
While, in an exposing head which scan-exposes a printing plate which is long in the sub-scanning direction, the exposing stage is also long. Therefore, a slight inclination or deformation of the exposing stage causes the light beams irradiating onto a printing plate to become out of focus.
Accordingly, in a scan-exposure device, highly accurate parts must be used for an exposing stage and for a mechanism which moves the exposing stage for scanning. Also, highly accurate adjustment at the time of assembling the exposing stage, and the like, are required.
Further, in a scan-exposure device, parts forming an exposing head expand or contract due to temperature changes. This causes light beams to become out of focus even when a highly accurate adjustment has been done at the time of assembly and this results in degradation of finishing quality, due to blur and the like, in an image formed on a printing plate.
In order to prevent light beams from becoming out of focus due to environmental changes such as temperature, a temperature control device such as a cooling device is required, and therefore production costs for the apparatus is increased. Particularly, since an exposing stage, in which light sources for exposing an image onto a printing plate and the like are arrayed in a line, is long, light beams are likely to become out of focus. Therefore, there is a need to prevent the light beams from becoming out of focus due to temperature changes. Also, adjustment needs to be facilitated at the time of assembly or when the light beams become out of focus.
In view of the aforementioned, an object of the present invention is to propose a scan-exposure device with an exposing head having a plurality of light sources arrayed in a line, in which focus adjustment of light beams is easily carried out and the extent to which light beams become out of focus due to temperature changes or the like is reduced.
A first aspect of the present invention is a scan-exposure device for irradiating a recording medium disposed on a support, the scan exposure device including: (a) a light source stage having opposite end portions and a plurality of light sources operable for producing light beams arrayed in a line for irradiating a recording medium disposed on the support; (b) a pair of bases, with one base supporting the stage in a vicinity of one end portion of the stage, and the other base supporting the stage in a vicinity of the other end portion; and (c) a positioning mechanism provided at each base, with each positioning mechanism operable for controlling distance between the recording medium and the stage independent of the other positioning mechanism.
A second aspect of the present invention is a scan-exposure device for irradiating a recording medium, the scan exposure device including: (a) a support for supporting a recording medium; (b) a plurality of light sources arrayed in a longitudinal direction of the support for irradiating the recording medium with light beams; (c) a stage provided so as to be movable in directions which are substantially parallel and substantially perpendicular to the longitudinal direction of the support, with the stage having the plurality of light sources fixed thereon and opposite end portions; (d) a base supporting the stage at each end portion thereof and movable in a direction substantially parallel to the longitudinal direction of the support; and (e) an adjusting mechanism operable for moving the stage toward and away from the recording medium on the support.
A third aspect of the present invention is a scan-exposure device for irradiating a recording medium while the recording medium is moving in a predefined direction, the scan-exposure device including: a light source stage having opposite longitudinal direction end portions and a plurality of light sources operable for emitting light beams, the light sources having a predetermined spacing along the longitudinal direction of the light source stage; bases provided for supporting the light source stage at the longitudinal direction opposite end portions thereof, and movable in a direction orthogonal to the predefined direction in which the recording medium moves; and a scan-moving device operable for moving the light source stage in the direction orthogonal to the predefined direction by moving one of the bases.
According to the present invention, longitudinal direction opposite end portions of a light source stage, having a plurality of light sources attached at predetermined positions thereon, are respectively supported by a pair of bases. These bases can respectively move in a scanning direction of the light sources at a time of scan-exposing.
A scan-moving device is attached to one of the bases, and as the scan-moving device moves the one of the bases in the scanning direction of the light beams, the light source stage moves in the scanning direction of the light beams.
Since the bases are separately attached to the light source stage, they can move relative to each other. Thus, for example, when the light source stage expands or contracts due to temperature changes, the bases move relative to each other so as not to cause deformation, or the like, of the light source stage.
Therefore, deformation of the light source stage can be prevented without using expensive cooling temperature control devices, and the light beams can irradiate appropriate positions on the recording medium.
Further, according to the present invention, distance adjusting devices are provided between the light source stage and the bases at the opposite end portions of the light source stage in order to enable the light source stage to move toward and away from the recording medium with respect to each of the bases, and to be retained at the position after being moved toward or away from the recording medium.
Thus, distances (spaces) between the recording medium and each of the longitudinal direction opposite end portions of the light source stage can be respectively adjusted, and this facilitates adjustment of distance between the light source stage and the recording medium and inclination of the light source stage with respect to the recording medium.
Furthermore, according to the present invention, distance measuring devices are provided at the longitudinal direction opposite end portions of the light source stage to enable detection of distances between the recording medium and the longitudinal direction opposite end portions of the light source stage.
This facilitates determining if the light source stage (i.e., light sources) is at an appropriate distance from the recording medium. In addition, distance and inclination of the light source stage with respect to the recording medium can be easily adjusted by moving the light source stage with the distance adjusting devices on the basis of the results of the measurements by the distance measuring devices.
As described above, by facilitating positioning (such as adjustment of distance and inclination) of the light source stage with respect to the recording medium, the light source stage can be appropriately positioned and assembled with respect to the recording medium even when accuracy in machining or assembly of parts thereof is relatively low. In addition, since the position of the light source stage can be adjusted with a periodic or arbitrary timing, image exposures can be carried out with appropriate focusing.